(i) Field of the Invention
The present invention relates to organic acid anion containing aluminum salt hydroxide particles, a production method thereof, and use thereof. That is, the present invention relates to organic acid anion containing aluminum salt hydroxide particles which can be used in various fields, such as fields of construction, food, agriculture, semiconductors, electrophotography, medical care, cosmetics, chemical, resins, fibers and rubber, and other industrial fields, and a production method of the particles. More specifically, the present invention relates to organic acid anion containing aluminum salt hydroxide particles which have a very small and uniform particle diameter, are in the shape of spheres, pairs, rectangular parallelepiped, disks (go stones), hexagonal plates, rice grains or cylinders and have low moisture absorbability and excellent addability to rubber or the like, and to a production method of the particles and use of the particles.
(ii) Description of the Related Art
A representative alunite compound is alunite. Natural alunite exists as alumstone in heat mineral deposits and acid-corroded areas formed by active volcanoes or hot springs. Synthetic alunite is used in the industry as an adsorbent, an additive to resins, a filler and various carriers. The following synthetic methods are known.
Publication 1 describes a method for synthesizing alumstone by mixing aluminum sulfate (Al2(SO4)3), potassium sulfate (K2SO4) and sodium sulfate (Na2SO4) in a given ratio and agitating the mixture continuously at 100° C. under atmospheric pressure for 48 hours by a magnetic stirrer equipped with a hot plate.
Publication 2 describes a method for producing alunite having a specific surface area of 200 to 240 m2/g by adding potassium sulfate (K2SO4) and potassium hydroxide (KOH) to an aluminum sulfate (Al2(SO4)3) aqueous solution to adjust the K/Al ratio to 5 and the pH to 3.7 and boiling and refluxing the solution for three hours. It has been reported that alunite produced by this method is a flake-shaped porous aggregate which has slits having a width of 15 to 30 Å and has water adsorbability comparable to that of silica gel and high adsorbability to SO2 and NO and adsorbs acidic dyes well.    Publication 1: Kawano et al., Mineralogy Journal, Vol. 20, Num. 1 and 2, pp. 13 to 23, January and April, 1991    Publication 2: Inoue et al., Journal of Chemical Society of Japan, 1985(2), pp. 156 to 162
As methods for producing alunite compounds at low cost and in good yield to use them as adsorbents in the industry, the following Publications 3, 4 and 5 are known.
Publication 3 (JP-A 64-11637 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) describes an alunite type adsorbent represented by the following formula:MM′3(SO4)2(OH)6(wherein M represents a monovalent cation, and M′ represents Al or a combination of Al and Fe(III)), and having a BET specific surface area of not smaller than 280 m2/g and a pore volume within a pore diameter of 100 to 300 Å of not smaller than 0.05 ml/g. As for synthesis thereof, a method in which when aluminum sulfate or a combination of aluminum sulfate and ferric sulfate and alkali sulfate are subjected to a heating reaction in an aqueous solvent containing alkali hydroxide, the pH of the reaction solution is kept at 4.0 to 4.4 from the start of the reaction and the pH of the reaction is kept at 3.8 or higher in the reaction process so as to crystallize an alunite type layered compound having an increased specific surface area is described.
Publication 4 (JP-A 64-11638) describes an adsorbent composition that comprises a homogeneous composition comprising a layered compound having a chemical structure represented by the following formula:MM′3(SO4)2(OH)6(wherein M represents a monovalent cation, and M′ represents Al or Fe(III)), and an alunite type or jarosite type crystal structure and amorphous silica or amorphous silica alumina whose amount is 5 to 80 wt % based on the layered compound and that has a BET specific surface area of not smaller than 300 m2/g and a pore volume of not smaller than 0.1 ml/g. Further, it is described with respect to a production method thereof that alunite type and jarosite type layered compounds can be crystallized depending on starting materials and the value of pH in the reaction.
Publication 5 (JP-A 2000-7326) describes a spindle-shaped or spherical alkali aluminum salt hydroxide that comprises independent particles, is represented by the following formula:MAl3(SO4)2(OH)6(wherein M is a monovalent alkali metal or an ammonium group), D25 and D75 satisfy:1.2≦D75/D25≦2when particle diameters at 25% and 75% values of volume-based cumulative particle size distribution curve by a Coulter method are represented by D25 and D75, respectively, and is specified by chemical composition, and X-ray diffraction images, the pH of 5% aqueous suspension, a BET specific surface area and moisture absorbability which are different from those of alunite. Further, in this publication, an alkali aluminum salt hydroxide whose parameters such as the bulk specific gravity of particles, a volume-based median diameter, the degree of sharpness of particle size distribution, an aspect ratio, a refractive index and the degree of abrasion are optimum with respect to compatibility with resins is proposed. As for a production method thereof, it is described that aluminum sulfate, alkali sulfate or ammonium sulfate and aluminum hydroxide are subjected to a hydrothermal treatment. Further, a method of controlling the shape of particles to either a sphere or a spindle is also suggested.
Meanwhile, Publication 6 (JP-A 6-122519) discloses a method for synthesizing “jarosite particles (amorphous water-containing ferric oxide particle powder)” which have spherical shapes, have an average particle diameter of 3 to 30 μm, a specific surface area BET value of 150 to 300 m2/g and a bulk density of 0.7 to 1.1 g/ml and are represented by the following formula:RFe3(SO4)2(OH)6 (R is K+, Na+, NH4+ or the like.)This publication proposes repetitive use of reaction mother liquor, i.e., “jarosite particles are produced by passing oxygen-containing gas through a mixed solution of a ferrous sulfate solution and a sulfate solution of alkali metal or ammonium ions to carry out an oxidation reaction within a temperature range of higher than 45° C. and not higher than the boiling point.”